Enhanced oil recovery profile control with crosslinked anionic acrylamide copolymer gels

Abstract

An aqueous polymeric gel-forming composition capable of selectively plugging highly permeable zones in subterranean oil-bearing formations. The composition comprises an aqueous solution of an anionic acrylamide copolymer of high molecular weight, comprising about 5 to 95 weight percent of 2-acrylamido-2-methylpropanesulfonic acid, about 2 to 95 weight percent of N-vinyl-N-methyl acetamide and about 5 to 93 weight percent of acrylamide, and a crosslinking agent selected from the group consisting of transition metal ions, phenolic resins and amino resins. The compositions of this invention will form stable gels in brines of wide-ranging salinity and are effective at the pH levels encountered in carbon dioxide and water flooding operations. Also provided is a process for selectively plugging regions of higher permeability within an oil-bearing formation to improve sweep efficiency during a fluid flood oil recovery operation.

What is claimed is: 
     
       1. An aqueous crosslinked acrylamide copolymer gel formed in the absence of a partial hydrolysis step, consisting essentially of: (a) water;   (b) a viscosifying amount of an anionic acrylamide copolymer of high weight-average molecular weight produced by copolymerizing an aqueous mixture of monomers comprising about 5 to 95 weight percent of 2-acrylamido-2-methylpropanesulfonic acid; about 2 to 95 weight percent of N-vinyl-N-methyl acetamide; and about 5 to 93 weight percent of acrylamide, said copolymer having a weight-average molecular weight of at least 5×10 6  and able to form a stable crosslinked gel without first subjecting said copolymer to a partial hydrolysis step;   (c) a crosslinking agent selected from the group consisting of transition metal ions, phenolic resins and amino resins wherein said crosslinking agent is present in an amount sufficient to cause gelation of the aqueous solution of said anionic acrylamide copolymer of high weight-average molecular weight and produce the crosslinked gel.   
     
     
       2. The gel of claim 1, wherein said crosslinking agent is said transition metal ions. 
     
     
       3. The gel of claim 2, wherein said transition metal ions are Cr +3  ions. 
     
     
       4. The gel of claim 3, wherein said Cr +3  ions are present in an amount of about 50 to about 750 ppm. 
     
     
       5. The gel of claim 1, wherein said crosslinking agent is an amino resin. 
     
     
       6. The gel of claim 5, wherein said amino resin is a condensate of formaldehyde and melamine. 
     
     
       7. The gel of claim 6, wherein said formaldehyde and melamine are present in a 3:1 molar ratio. 
     
     
       8. The gel of claim 7, wherein said amino resin is present in an amount of 0.02 to 5.0 weight percent. 
     
     
       9. The gel of claim 1, wherein said crosslinking agent is a phenolic resin. 
     
     
       10. The gel of claim 9, wherein said phenolic resin comprises about 1 to about 99 weight percent of at least one phenolic compound selected from the group consisting of phenol, resorcinol, catechol, phloroglucinol, pyrogallol, 4,4'-diphenol and 1,3-dihydroxynaphthalene; and about 1 to about 99 weight percent of at least one aldehyde component selected from the group consisting of aliphatic monoaldehydes, aromatic monoaldehydes, aliphatic dialdehydes and aromatic dialdehydes. 
     
     
       11. The gel of claim 10, wherein said phenolic compound is resorcinol and said aldehyde component is formaldehyde. 
     
     
       12. The gel of claim 11, wherein said phenolic resin is present in an amount of about 0.02 to about 5.0 weight percent. 
     
     
       13. The gel of claim 12, wherein said copolymer is present in an amount of about 0.05 to about 1.0 weight percent. 
     
     
       14. The gel of claim 13, wherein said water is a brine.